Muon ${g-2}$ discrepancy within D-brane string compactifications

TL;DR

This paper investigates how D-brane string theory contributions, especially from anomalous U(1) gauge bosons and Regge excitations, could explain the muon g-2 discrepancy, considering experimental constraints and model specifics.

Contribution

It analyzes the potential of D-brane string theory, including anomalous U(1) bosons and Kaluza-Klein modes, to account for the muon g-2 anomaly within experimental bounds.

Findings

Anomalous U(1) gauge bosons can partially reduce the g-2 discrepancy.

Regge excitations are strongly suppressed and unlikely to explain the anomaly.

KK modes on lepton branes can evade LHC bounds and bridge the g-2 gap.

Abstract

Very recently, the Muon $g-2$ experiment at Fermilab has confirmed the E821 Brookhaven result, which hinted at a deviation of the muon anomalous magnetic moment from the Standard Model (SM) expectation. The combined results from Brookhaven and Fermilab show a difference with the SM prediction $\delta a_\mu = (251 \pm 59) \times 10^{-11}$ at a significance of $4.2\sigma$, strongly indicating the presence of new physics. Motivated by this new result we reexamine the contributions to the muon anomalous magnetic moment from both: (i)~the ubiquitous $U(1)$ gauge bosons of D-brane string theory constructions and (ii)~the Regge excitations of the string. We show that, for a string scale ${\cal O} ({\rm PeV})$, the contribution from anomalous $U(1)$ gauge bosons which couple to hadrons could help to reduce (though not fully eliminate) the discrepancy reported by the Muon $g-2$ Collaboration. Consistency with null results from LHC searches of new heavy vector bosons imparts the dominant constraint. We demonstrate that the contribution from Regge excitations is strongly suppressed as it was previously conjectured. We also comment on contributions from Kaluza-Klein (KK) modes, which could help resolve the $\delta a_\mu$ discrepancy. In particular, we argue that for 4-stack intersecting D-brane models, the KK excitations of the $U(1)$ boson living on the lepton brane would not couple to hadrons and therefore can evade the LHC bounds while fully bridging the $\delta a_\mu$ gap observed at Brookhaven and Fermilab.